Caption: Biomedical illustration of G protein coupled receptor and G protein. The G protein receptors span the bilipid cell membrane and are involved in nearly every physiological function. They react to stimuli from a variety of sources including light-sensitive compounds, odors, pheromones, hormones and neurotransmitters. They undergo a conformational change which activates an associated G protein. The G protein consists of three parts: alpha, beta and gamma, each of which may have a separate function within the cell. Here, the alpha portion activates the enzyme adenylate cyclase and the beta-gamma complex activates an ion channel. Because they are involved in many diseases, G protein coupled receptors are the targets of nearly 50% of all modern medicinal